Full flow leaching pit

ABSTRACT

The infiltrative capacity and fluid storage capacity of leaching trenches, beds, and pits (collectively called leaching &#39;&#39;&#39;&#39;fields&#39;&#39;&#39;&#39; herein) are increased by means of fluid accumulators placed within the field and spaced from the side and bottom walls thereof by infill (crushed stone, gravel stone, etc.). Effluent discharged to the field accumulates in the infill until it exceeds a predetermined level with respect to the accumulators and then proceeds to fill the accumulators. When the effluent level in the infill later subsides, effluent is discharged from the accumulators into the infill for drainage into the soil.

United States Patent [1 1 Sullivan FULL FLOW LEACHING PIT [76] Inventor: A. Eugene Sullivan, 138 Fells Ave,

Medford, Mass. 02155 [22] Filed: May 20, 1974 21 App]. No.: 471,325

[52] US. Cl. 61/11; 61/13; 210/170 [51] Int. Cl. E02B 11/00 [58] Field of Search 61/10, l1, 12, 13; 2l0/l7,

[56] References Cited UNITED STATES PATENTS 553,424 l/1896 Ricks 210/117 1,025,079 4/1912 Wells 61/10 UX 1,917,805 7/1933 McManus... 210/1 17 2,126,575 8/1938 Ranney 61/11 X 3,425,226 2/1969 Santeford.... 61/13 3,645,100 2/1972 LaMonica 61/13 Nov. 18, 1975 3,762,437 10/1973 King ..6l/13X Primary Examiner-Dennis L. Taylor Attorney, Agent, or Firm-Cesari and McKenna [57] ABSTRACT The infiltrative capacity and fluid storage capacity of leaching trenches, beds, and pits (collectively called leaching fields herein) are increased by means of fluid accumulators placed within the field and spaced from the side and bottom walls thereof by infill (crushed stone, gravel stone, etc.). Effluent discharged to the field accumulates in the infill until it exceeds a predetermined level with respect to the accumulators and then proceeds to fill the accumulators. When the effluent level in the infill later subsides, effluent is discharged from the accumulators into the in- ,fill for drainage into the soil.

32 Claims, 16 Drawing Figures US. Patent Nov. 18, 1975 SheetlofS 3,919,848

US. Patent Nov. 18, 1975 Sheet20f5 3,919,848

US. Patent Nov. 18, 1975 Sheet 3 of5 3,919,848

FIG.9

US. Patent Nov. 18, 1975 Sheet 5 of5 3,919,848

FIG.I5

FE.B FEGJG FULL FLOW LEACI'IING PIT BACKGROUND OF THE INVENTION A. Field of the Invention The invention relates to leaching fields and, more particularly, comprises an improved form of leaching field, as well as structures for use therein.

B. Prior Art Leaching fields in the form of trenches, pits or beds are in common use to discharge the effluent from a septic tank or waste water treatment facility into the soil for filtration and subsequent run-off into undergound fluid channels. typically, these fields are formed from an appropriately shaped void which is subsequently filled in with various layers of crushed stone, gravel stone or rock (hereinafter callectively called *stone). The stone provides a porous infill and separates the soil surfaces of the void from direct contact with an effluent discharge element such as a porous pipe which receives effluent from a septic tank, dosing tank, or other source and discharges it into the infill for subsequent infiltration into the earth.

In the case of leaching pits, the discharge element is a porous tank; in the case of leaching trenches, or beds the discharge elements are one or more porous pipes placed within the infill and running along the length of the trenches or beds. A typical trench is 30 inches'wide, 36 inches deep and 75 feet long and filled with stone; a wider trech, commonly called a gallery", is of the order of 6 feet wide and 6 feet deep and is also filled with stone. A typical pit may be up to 10 feet in diameter and 6 feet deep and uses construction block to form a porous, generally cylindrical wall through which effluent flows into the soil.

The leaching or infiltrative capacity of pits and trenches depends on the infiltrative capacity of both the side and bottom walls of the pit or trench. As the pits and trenches age, however, the bottom wall or face becomes less and less porous and the side walls or faces assume increasing importance. This is especially the case in a leaching pit. However, in present pits and trenches, this side wall capacity is greatly under-utilized, since the effluent infiltrates these sidewalls only when enough of it has been discharged into the void (loading) to raise the effluent levelwithin the void to a height sufficient to cover the sidewalls. In contrast, the bottom face of the pit ortrench, as well as the lower side wall surfaces, are wetted during each loading and .therefore perform a major share of the leaching or filtering during the early stages of their existance. This hastens the failure of these surfaces, since they thereby accumulate an excessive amount of particulate material from the effluent. The deterioration process is regenerative, that is, as the infiltrative capacity of the bottom and lower portion of the side wall surfaces deteriorates, effluent discharged into the void covers these surfaces for increasingly longer periods of time before adsorption. The flooded surfaces are thus maintained under anaerobic conditions which greatly retard the decomposition of the organic constituants of the effluthe wider trenches or pits, it is necessary to construct a larger number of them and this increases the cost of the disposal system. Also, this requires additional pipelines and somewhat more complicated fittings such as distribution boxes, and this further adds to the cost. Further, there are practical lower limits to the trench or pit widths which can be dug with equipment current in use, as well as limits on the number of trenches or pits which can be dug in the generally limited disposal area.

Leaching beds, in contrast, are characteristically shallow voids of broad lateral and longitudinal extent. Typically, such a bed is of the order of 18 inches in depth and may be 50 feet or more in width and length. Formerly the voids were filled in with stone, but this has been superseded by the use of precast chambers having generally open side and end walls butted together side by side and end to end to cover the bottom (infiltrative) surface of the bed. This exposes the entire infiltrative surface to the effluent within the chambers. However, unless the bed is loaded with a very high loading, infiltration of the effluent frequently tends to occur predominantly in the vicinity of the effluent discharge source and thus the field is not loaded uniformly.

SUMMARY OF THE INVENTION A. Objects of the Invention Accordingly, it is an object of the invention to provide an improved leaching system.

Further, it is an object of the invention to provide a improved leaching trench, bed or pit.

Yet a further object of the invention is to provide an effluent accumulator for leaching trenches, beds, and pits.

Still a further object of the invention is to provide an effluent accumulator for a leaching field to temporarily store effluent during periods of high loading and release it during periods of decreased loading.

Another object of the invention is to provide an effluent accumulator whose operation is self-adjusted to the infiltrative capacity of the leaching void in which it is placed.

Still another object of the invention is to provide a leaching field system which more effectively distributes effluent over vertical soil interfaces.

B. Brief Description of the Invention In accordance with the present invention, I more effectively utilize the side wall infiltrative capacity of leaching trenches and pits, and provide a more uniform loading of leaching beds, by constructing the trenches, beds or pits (hereinafter simply called fields) with the aid of a number of hollow accumulators placed within the fields to store effluent during periods of high loadings, and subsequently release it during periods of lesser loadings. These accumulators are in the form of covered cisterns preferably having bottom, side and top walls. They are placed directly in the leaching voids and are spaced apart from the side walls of the void, and typically from the bottom walls also, by means of a narrow layer of i'nfill having a correspondingly small fluid holding capacity.

The accumulators occupy a substantial portion of the excavated volume of the field, so that the available free volume of the excavated void exterior to the accumulator is quickly filled by a much smaller effluent loading than is the case without them. When so filled, the side walls are completely wetted and the effluent infiltrates, or permeates, through them and through the bottom faces of the excavated void at loadings that previously would have been adequate for wetting the bottom face alone. Further, each accumulator, being hollow, has an effluent storage capacity substantially greater than that of the infill it displaces. When a loading in excess of the storage volume of the exterior void is applied to the field, the excess is temporarily stored in the accumulators and then released to the void as the effluent level diminishes. Thus, not only is the excess loading accomodated, but the effluent within the exterior void is replenished from the accumulators as it recedes; this tends to maintain the wetting of the side walls for a longer time.

In a preferred embodiment of the invention, each accumulator has at least one fluid inlet channel extending through an upper side wall or top wall, together with at least one fluid outlet channel at a lower level in a side or bottom wall of the accumulator. The fluid outflow channel is constructed to either partially or fully restrict fluid in flow to the accumulator when theeffluent level in the void exterior to the accumulator is rising and to allow free outflow when this level again recedes. Full restriction is accomplished by means of a one-way valve positioned to open outwardly of the accumulator and responsive to a difference in hydrostatic head between the effluent exterior and interior to the accumulators to close and prevent fluid inflow when the exterior effluent level is higher than the effective interior level and to open and allow fluid outflow when thereverse condition prevails. The valve is effectively a static type of restriction. Partial restriction is accomplished by restricting the cross section of the outlet channel to thereby restrict the flow rate through it; its effectiveness depends on filling the void exterior to the accumulator at a rate much faster than the rate at which any significant amount of effluent can flow into the accumulator through the orifice. This is essentially a dynamic type of restriction.

In accumulators using valves, as long as the fluid level in the void exterior to the accumulator is below that of the accumulator fluid inlet channel, no effluent passes into the accumulator. However, when the outside effluent level reaches the level of the fluid inlet channel, it begins to spill into the accumulator where it is temporarily stored. The outlet channel valve is held closed during this time, preferably by means of the difference in hydrostatic head between the exterior and interior much slower rate than that at which it was applied to the exterior void. Concurrently, a slow equalizing fluid flow occurs through the outlet orifice, this flow being into the accumulator as long as the exterior fluid level is above the interior fluid level (positive head) and out of the accumulator as long as the exterior level is below the interior level (negative head).

In another form of accumulator, a siphon takes the place of the inlet and outlet channels. This siphon is preferably formed within the walls of the accumulator, and has a first vertically extending leg terminating within the accumulator at its bottom end and horizontally bridged at its upper end to a second vertically extending leg terminating exterior to the accumulator at its lower end. A trap (which may be formed by a U- shaped bend in the lower end of the exterior leg of the siphon) prevents blockage by air bubbles forming in the bridge. As the effluent in the void exterior to the accumulator rises, the effluent level within the exterior (second) siphon leg raises correspondingly until it reaches the level of the horizontal bridge and then starts to flow downwardly into the accumulator through the interior (first) leg. Thereafter, the accumulator receives and stores the remainder of the effluent loading. When the exterior level recedes to a level below that within the accumulator, reverse flow takes place and the accumulator discharges its contents into the exterior void, the interior level following the exterior level downwardly as it does so. The operation is thus similar, though not identical, to that of the valved or restricted orifice accumulators, and, again, the side wall surfaces of the void are wetted over a substantially longer period than would normally be the case.

The accumulators may be supplied in any desired size or shape. Advantageously, however, they comprise shallow, elongated, cisterns of generally rectangular or even somewhat V-shaped cross section in the case of leaching trenches and beds, and somewhat deep cisterns of cylindrical rectangular or even V-shaped cross sections in the case of leaching pits. Preferably, they are of precast concrete or other durable material, and

- may be formed in two or more sections (i.e., roof and of the accumulator. When the outside effluent level again recedes and drops to a level below that of the stored effluent in the accumulator, the valve in the outlet channel opens and effluent flows out from the accumulator through this channel and into the infill within the void. The outflow continues until the accumulator is emptied or until the next loading of sufficient volume to bring the outside level above the accumulator level. Thus, with each loading, the sidewalls of the field are wetted to a substantially greater height than is the case in present systems. Further, this is accompanied by a substantial increase in the storage capacity of the field.

In accumulators using an outlet channel of restricted size, during dynamic conditions in which the effluent level exterior to the accumulator is rapidly changing, little effluent flows into the accumulator until the exterior level rises to the level of the inlet channel. The accumulator then fills with the excess effluent. When the loading ceases, quasi-static conditions are approached during which the effluent exterior to the accumulator begins leaching into the earthen surface, typically at a side and bottom surfaces) to facilitate manufacture; a covered manhole extending through the roof facilitates inspection and maintenance. However, many variations are possible; for example it is possible to omit the bottom wall and rest the side walls directly on or in the soil, relying on the limited bottom soil porosity to contain the excess effluent for a time period.

Two or more accumulators may be vertically stacked to further increase the wetting of the upper side wall areas. In this configuration, the accumulators are each of much less vertical extent then the excavated void in which they are placed and are interconnected so that effluent is supplied to a lower accumulator only after the preceding upper accumulator is filled. For this purpose, each is supplied with an outlet channel, but only the uppermost accumulator has an inlet channel. Thus excess effluent is stored at the highest level first, as opposed to filling the accumulator fromthe bottom up as in the case of a single, deeper accumulator. As the effluent recedes, the accumulators empty in sequence, the uppermost first. The stacked accumulators have the effect of reducing the effective exterior hydrostatic head which the upper accumulators see, and these thus discharge their contents at a higher level on the side wall, thus further facilitating upper side wall wetting.

Fields using the accumulators are most advantageously loaded with the aid of dosing tanks. These provide a measured loading which can be adjusted to load the exterior voids to a predetermined height,'e.g. to the level of the fluid inlet channels of the accumulators within the field. Under normal loading conditions, the field is preferably designed and proportioned so that the loading in a given part of the field substantially completely permeates into the field surfaces prior to a further loading. During periods of higher than normal use, the accumulators then perform their temporary storage function. I

DETAILED DESCRIPTION OF THE INVENTION The foregoing and other and further objects and features of the invention will be more readily understood on reference to the following detailed description of the invention when taken in conjunction with the accompanying drawings in which:

FIG. 1 is a pictorial illustration of a trench-type leaching field constructed in accordance with the present invention;

FIG. 2 is a cross sectional view taken along the lines 2-2 of FIG. 1;

FIG. 3 is a view in perspective of the accumulator of FIGS. 1 and 2, with portions broken away for clarity;

FIG. 4 is a side sectional view of 'a simple form of valve that may be used in the present invention;

FIG. 5 is an enlarged, fragmented vertical sectional view along the lines 5-5 of FIG. 2 and illustrating a preferred form of valve construction in accordance with the present invention;

FIG. 6 is a view in perspective of the valve of FIG. 5;

FIG. 7 is a view in perspective of an accumulator for use in wide, deep trenches known as galleries;

FIG. 8 is a pictorial view of a pit type of leaching field constructed in accordance with the present invention, with portions of one of the accumulators used therein broken away for clarity;

FIG. 9 is a vertical sectional view along the lines 99 of FIG. 8;

FIG. 10 is a view in perspective of a leaching bed constructed in accordance with the present invention;

FIG. 11 is a vertical sectional view along the lines 11l1 of FIG. 10;

FIG. 12 is a vertical sectional view of an accumulator having a restricted orifice instead of a valved outlet channel;

FIG. 13 is a vertical sectional view of an accumulator [having a siphon instead of inlet and outlet channels;

FIGS. 14 16 are vertical sectional views of still other forms of accumulator in accordance with the present invention.

In FIG. 1, a septic tank or waste water treatment facility receives effluent from a house or other facility (not shown) and applies it to a dosing tank 10 for carriage to a distribution box 12 and thence through pipes l4, l6, l8 and 20 to a series of trenches 22, 24, 26 and 28 for disposal there by infiltration into the earth. A typical trench is shown in cross section in FIG. 2. The trench 22 comprises an excavated void having one or more generally rectangular cisterns or accumulators 30 centrally disposed therein and surrounded by crushed rock or gravel 32. A layer of filter sand 34 may be positioned at the bottom of the trench. Pipe 14 carries the effluent from the distribution box 12 into the trench 22 and distributes it along the length thereof through openings such as aperture 14a and 14b in that portion of the pipe within the trenches. Pipe of this nature is commonly used in subsurface sewage disposal systems and is frequently of a type known as Orangeburg pipe or is of vitrified clay having perforations along its extent. This pipe is positioned within the in-fill of crushed rock exterior to the accumulator, and the trench is then covered to grade with a layer of selected backfill 36.

Alternatively, the effluent may be carried along the trench by means of built in fluid channels 38 forming troughs'which carry the effluent and having projections 38a and indentations 38b which mate with each other when aligned to carry effluent down a row of accumulators. When these channels are provided the effluent is applied directly to them from the distribution box 12.

The accumulator 30, which is shown more clearly in FIG. 3, has a bottom wall 42, side walls 44, and the top wall of roof 46. Fluid inlet channels 48 are formed in the side walls of the accumulator adjacent the top thereof; corrspondingly, fluid outlet channels 50 are formed in the side walls of the accumulator at the bottom thereof. These channels comprise apertures extending through the walls of the accumulator to allow liquid flow therethrough. The fluid inlet channels are open, that is, unobstructed to fluid flow; however, as shown more clearly in FIG. 4 through 6, the fluid outlet channels include valves in them which prevent the inflow of liquid but which, when opened, allow the outflow of liquid. A manhole 51 having a cover 53 provides access to the interior of the accumulator.

A simple form of such a valve is shown in FIG. 4 and comprises a thin cylindrical flapper plate 52 having a projecting tab 54 on a portion of its periphery which snugly fits into a slot 56 (shown exaggerated in size for clarity) in the wall of the fluid outlet channel 50. The tab and flapper plate are advantageously formed integral with each other and from a tough, flexible, resilient material such as a polypropylene. The channel 50 is in the form of a stepped outwardlyflaring cone having an intermediate lip 58 against the face of which the outer periphery of the back face of the flapper 52 abuts. When the force exerted by the fluid on the exterior of the accumulator (the exterior being on the right in FIG. 4) is greater than that exerted by the fluid within the accumulator (the interior of'the accumulator being on the left in FIG. 4), the rear peripheral face of the flap 52 abuts tightly against the face of lip 58 to thereby form a fluid-tight seal which prevents fluid from escaping from the interior of the accumulator. When the force exerted by the fluid on the exterior is less than that exerted by the fluidon the interior due to the different heads or effluent levels, the flapper plate 52 pivots about the tab 56 to thereby open and discharge stored effluent from the accumulator. A screen 60 closes off the outer section of channel 50 from the infiltration of stone and other large materials which would prevent opening of the valve but otherwise allows relatively unimpeded fluid flow through it.

As effluent is discharged into the trench 22 through pipe 14, it fills the bottom of the trench and then starts rising so as to wet the side walls. When the effluent level of the trench reaches the level of the fluid inlet channel 48, it ceases rising in the trench and instead begins to fill the accumulator 30. This prevents surface breakthrough caused by excessive loading. For this purpose, the fluid-storage capacity of accumulator 30, together with that of the trench 22 up to the level of the inlet channels 48, should be sufficient to accomodate the normal loading applied to the stone 32. This will insure that effluent breakthrough at the surface does not occur. Indeed, because the infiltrative capacity of all leaching surfaces decreases with time, it may be desirable to have the accumulative capacity of the accumulator 30 somewhat larger than the design value calculated from the initial maximum anticipated loading, so as to allow for the retention of effluent from one loading to another within the void exterior to the accumulator which occurs as the infiltration surfaces age.

As long as the effluent level exterior to the accumulator is greater than the effluent level within the accumulator, the outlet valve in the fluid outlet channel 50 remains closed and effluent does not flow out from the accumulators. When, however, the exterior effluent level drops below that within the accumulator, effluent flows outwardly from the accumulator and discharges into the crushed stone surrounding the accumulator. Thus, the valve responds to the difference in height between the levels within and outside the accumulator and the accumulator acts as a controlled effluent-dosing device, storing effluent when the level in the trench exceeds a certain height and discharging it when the effluent level again drops below the interior level. In this respect, the accumulators are condition-responsive to their environment. The infiltration capacity of various trenches will change as a function of time, and this change may be a somewhat different function for each of the trenches. Regardless of this change, however, the

accumulators always sense the effluent level within the trenches in which they are placed and respond by first storing and subsequently releasing effluent to maintain a substantial side wall setting over a longer interval than would be the case without them.

A preferred from of valve is shown in FIGS. 5 and 6 and comprises a generally cylindrical glange 60 having a flapper plate 62 attached thereto by means of a pivot 64. A generally circular groove 66 in the face of the plate 62 seats an O-ring 68 which butts against a flat face 70 of the flange 60. .The plate 62, when seated against face 70 of flange 60, closes off a generally cylindrical fluid channel 72 extending through the flange and prevents fluid flow therethrough. A finger 74 from the rear face of the flapper plate 62 and limits movement of the flapper plate when it pivots (in a clockwise direction) about pivot 64.

The valve 60 is attached to the channel 50 on the interior side thereof by means of threaded bolts 76 extending through apertures 77. The remote ends of the bolts are seated in the wall of the accumulator by means of a hardenable sealing compound 78 or are set in during molding. A collar 80 butts against the interior wall of the accumulator and may be embedded therein; it provides a generally flat surface against which a washer 82 rests. One face of the flange 62a is pressed tightly against the washer 82 by means of the bolts 76 and nuts 84 threaded on these bolts.

As presently contemplated, the accumulator of the type shown in FIG. 3 is advantageously formed of concrete and has exterior dimensions of 8 feet long, 24 inches wide, and 30 inches high interior dimensions of approximately 18 inches by 18 inches (thereby providing side and bottom walls 3 inches thick and a top face 9 inches thick), and fluid outlet channels located approximately 15 inches above the interior bottom face. The accumulator is located in a leaching trench approximately 36 inches wide and 45 inches high. It is laterally centered in the trench so that its outside walls are approximately 6 inches from the adjacent side walls of the trench. It is vertically spaced approximately 6 inches above the bottom space of the trench. The void within the trench exterior to the accumulator is filled with crushed stone to the level of the top of the accumulator or or even somewhat above this level, and the trench is back-filled with selected backfill to grade. A manhole approximately l2 inches in inside diameter extends between the interior of the accumulator and grade. Because the stone in the void is somewhat porous (typically having a porocity of 0.40) effluent discharged into the trench on either side of the accumulator in sufficient volume is able to fill the trench on both sides of the accumulator because of the porous connecting underpassage through the stone beneath the accumulators.

With the dimensions above stated, the leaching trench of the present invention has a total leaching area per linear foot along the trench of 7 square feet, namely, a bottom leaching area of 3 square feet and a side wall leaching area (measured up to the invert of the inlet channel) of an additional 4 square feet for a total of 7 square feet. A conventional trench of the same dimensions requires approximately 21 gallons per linear foot to wet the bottom and side wall faces in contrast to approximately 12 gallons in the present invention. Further, the conventional leaching trench has a total effluent storage volume per linear foot of approximately 21 gallons, while the trench of the present invention has a storage capacity in excess of 26 gallons. Thus, the trench of the present invention requires smaller loadings to wet the side wall areas for leaching but has a much greater effluent storage capacity so that it is capable of taking loadings substantially greater than those which can be taken by the conventional trench.

Turning now to FIG. 7, an accumulator that is expressly adapted for use in wider trenches or galleries is shown. The accumulator has a bottom wal 102, side walls 104 and a top wall 106. A manhole 108 extends through the top wall in the vicinity of an outlet channel 110; an inlet channel 112 is provided at the upper wall of the accumulator. Effluent transfer channels 114, 116 are formed integrally with two of the side walls at the upper ends thereof. Channel 114 has a tapered end section 118 for receiving the end of a preceding accumulator which carries effluent to the channel 114 and a tubular extension 120 which nests with a subsequent accumulator to pass effluent to the channel of that accumulator. As was previously the case, the outlet channel 110 has a one-way valve in it to restrict fluid flow. The fluid channel 116 is constructed in a similar manner and will not be described further. The accumulators 100 are placed end to end, and they are spaced from the bottom and side walls thereof by crushed stone, as was the case with the accumulators of FIGS. 1 through 3.

Typical dimensions presently contemplated for the accumulator 100 are a width of 5 feet, a height of 4% feet, and a length of 5 feet. The bottom and side walls are 4 inches thick and the top roof is 8 inches thick. The manhole 108 has an inside diameter of 2 feet and provides access to the interior of the accumulator for inspection and maintenance of the accumulator and outlet channel valve.

FIGS. 8 and 9 show an alternate form of the present invention as embodied in a leaching pit. As there shown, a distribution box receives effluent via a pipe 152 from a dosing tank (not shown) and discharges it to a number of leaching pits (illustratively shown as three in number) 154, 156, 158 via pipes 155, 157, 159. A cross section of the pit.156 is shown in detail in FIG. 9. The pit 156 has an accumulator in the form of a hollow cistern 160 having a bottom wall 162, a side wall 164, and a top wall or roof 166. A fluid transfer channel 168 in the form of a trough is formed integral with the side wall at the upper portion thereof and has open channels 170 through which effluent is carried to the pit 156. Effluent is carried to the channel 168 by pipe 157. (The channel 168 may, of course, be omitted and effluent deposited in the pit directly by pipe 157). Fluid inlet channels 172 are formed at the upper portions of the side walls, while fluid outlet channels 174 are formed at the lower portions of the side walls; the outlet channels have valves 175, for example, of the type shown in FIGS. 4 and 5, incorporated therein. The accumulator is spaced laterally from the side walls 180 of the pit, as well as vertically from the bottom face 182 of the pit, by a layer 184 of crushed rock.

As was previously the case with the leaching trenches, the effluent rises in the gravel layer 184 until its level reaches that of the fluid inlet channel 172, at which time it begins to spill into the accumulator 160 for storage. When the outside effluent level (the level in the stone 184) recedes, the valves 175 open to discharge fluid into the stone for infiltration into the side and bottom faces of the pit. The operation of this form of the invention is substantially identical to that of the leaching trench described earlier, and thus need not be described in further detail.

As a specific example of this embodiment of the invention, the accumulator 160 may take the form of a cylindrical tank 6% feet high and 8 feet in diameter. The side and bottom walls are 5 to 6 inches thick and the top wall nine inches thick, and the tank is advantageously formed of concrete. The bottom of the fluid inlet port is located 5 feet above the inside bottom face of this accumulator. The accumulator is spaced from side and bottom walls of the pit by 6 inches of stone. A

conventional leaching pit 6% feet deep and 8 feet in diameter has the same available bottom and side wall leaching area (approximately 230 square feet) and the same storage capacity (approximately 1,900 gallons); however, the conventional leaching pits requires a substantially greater loading (1,900 gallons) to wet the side wall faces as well as the bottom face than the leaching pit of the present invention which requires only approximately 445 gallons to accomplish this, Thus, substantially smaller loadings are required to wet the side wall faces with the present invention, as contrasted to conventional leaching pits.

The accumulators of the present invention may also be used in leaching beds. In this application, the accu mulators are placed side by side and end to end and are spaced by layers of stone from the side and bottom faces of the bed. An example of this is shown in FIGS. 10 and 11 in which a number of accumulators 200a-i are placed side by side and end to end on a stone layer within a leaching bed. The units are similar to those shown in FIGS. 1 through 3. They may have jutting lips 202 around the upper periphery thereof to thereby laterally space each chamber slightly from the other chambers to thereby prevent blockage of the inlet and outlet channels of each chamber by the adjacent cham-.

ber. The accumulators are suppliedwith effluent in the usual manner from pipes 210, 2-12, 214 from a distribution box or dosing tank 216 which in turn is fed from a septic tank (not shown) or other effluent source.

The accumulators 200 function in the manner previously described, that is, effluent is applied to the distribution channels within the accumulators and these channels distribute the effluent to the stone-filled void exterior to the accumulators. When the level of effluent in this stone layer rises to the level of the inlet channel, the accumulators begin to fill and retain the effluent until the outside level again drops, at which time the accumulators discharge their contents to the stone-filled void.

FIGS. 12 through 16 show still further variations of the accumulators of the present invention. In FIG. 12, an accumulator 220, such as of the type shown in FIGS. 1 through 3, is in the form of an elongated cistern of generally rectangular cross section having the usual distribution channels 222, 224 at the upper portion thereof, and fluid inlet channels 226, 228 extending through the side walls. In place of the expected outlet channel of FIGS. 1 through 3, however, the accumulator 220 has one or more restricted orifices 230 adjacent to the bottom thereof and extending through the sidewalls. The orifices 230 may advantageously by cylindrical or even somewhat tapered in shape, with an effective cross section of quite limited size, such as fractions of an inch.

It will be understood that the size of the orifice de-' pends on the rate at which effluent is to fill the void in which the accumulator is placed, and the rate at which the effluent level thereafter recedes on permeating into the surrounding soil. It is dimensioned such that only a small fraction of the effluent loading applied to the trench can flow from the trench into the accumulator through the orifice while the level in the exterior void is rising to the level of the inlet channel 226, but must be large enough to allow a reasonable outflow rate from the accumulator through this orifice when the effluent level again drops. Thus, the precise orifice size will be a compromise between these two variables. The accumulators otherwise function in the manner described in connection with the accumulators in the preceding figures, and will not be described in further detail.

FIG. 13 is a cross section of a further embodiment of the invention, having the shape of an elongated cistern of generally rectangular cross section in which the inlet and outlet channels are replaced by a siphon. The accumulator 250 has fluid distribution channels 252, 254 in the upper portion thereof and a siphon 256 in one of the sidewalls thereof. The siphon has a U-shaped 256 trap 258 in a lower portion thereof to prevent possible blockage of the siphon by trapped air bubbles.

The operation of the siphon is such that effluent rises in the stone-filled void exterior to the accumulator 250 when it is placed in a trench until the exterior effluent level reaches the height of the invert 260 of the siphon 256. When this occurs, effluent starts flowing into the accumulator 250. The flow thereupon continues once initiated, so as to tend to equalize the respective hydrostatic heads exterior to, and interior of, the accumulator. As the exterior level recedes, the accumulator replenishes it until its contents are fully discharged.

It should be noted that for loadings which are not substantially greater than normal, this form of accumulator may actually lower the fluid level exterior to the accumulator during loading when the siphon action starts.

In FIG. 14, which is a vertical cross sectional view of a further form of accumulator in accordance with the present invention, an accumulator 300 has a bottom wall 302, side walls 304, a roof 306, and a covered manhole 308 extending through the roof. Distribution channels 310 are formed in the roof 306. The side walls 304 slant inwardly toward the bottom of the accumulator so that the horizontal cross section of the accumulator progressively decreases going from the top to the bottom. Inlet channels 312 and an outlet channel 314 are formed in the side walls. A one-way valve, 316 is formed in the outlet channel 314. The accumulator is preferably placed in a correspondingly tapered trench or pit.

As noted previously, the outlet channel valve operates on the difference in effective hydrostatic head between the exterior of the accumulator and the interior of the accumulator. Regardless of the cross section of the accumulator, the interior head seen by the valve 316 depends only on the level of the effluent within the accumulator above this valve. However, the height of the center of gravity of the effluent within the accumulator depends directly on the cross-sectional shape of the accumulator. By tapering the accumulator inwardly at the bottom portion thereof, as shown in FIG. 14, the effective center of mass is raised to a greater height than it is in an accumulator with a rectangular cross section such as is shown in FIGS. 1 through 3. Thus, for a given fluid storage capacity, the effective center of gravity is at a higher potential energy in the accumulator of FIG. 14. This means that effluent begins to flow outwardly from the accumulator 300 at a correspondingly greater effluent level than is the case with an accumulator of non-tapered cross section. The taper of the accumulator of FIG. 14 is approximately 30 degrees. This represents a reasonable compromise between the incremental increase in effluent center of gravity obtained by tapering the accumulator and the increased difficulty of forming a tapered trench or pit.

Another way in which the effective center of gravity of effluent within an accumulator can be elevated is shown in FIG. 15 in which first and second accumulators 350, 352 of generally rectangular cross section are vertically stacked on one another, eg in an elongated trench as 354 as shown in FIG. 15. Accumulator 350 has a bottom wall 356, side walls 358, and a top wall 360. Inlet and outlet channels 362, 364, respectively, are formed in the side walls 358, and a one-way valve 366 is positioned in the outlet channel 364. Fluid distribution channels 368 are formed in the upper wall 360. These channels receive effluent from a source such as a distribution box or from preceding accumulators, and distribute it to the exterior void 354. The lower accumulator 352 has an outlet channel 370 only; a one-way valve 372 is placed in this outlet channel. An overflow pipe 374 interconnects the accumulators 350 and 352. The pipe 374 is so positioned that effluent must fill the accumulator 350 to the level of the top 374a of this pipe before it begins to spill into the lower accumulator.

The operation of the accumulators 350, 352, is as follows: Assume that both of these accumulators are initially empty and that a loading has just been applied to the void 354. The effluent level in this void rises to wet the side walls until it reaches the level of the inlet channel 362. At this point, it begins spilling into the accumulator 350. The level within this accumulator continues to rise toward the top 374a of the overflow pipe 12 374. If the loading ceases before the effluent level within the accumulator 350 reaches the top of this pipe, none of the effluent in the accumulator 350 is passed to the accumulator 352. If, however, the loading continues so that the effluent levels within the accumulator 350 reaches the top 374a of the overflow pipe, effluent begins to spill into the lower accumulator as long as the loading is applied. When the loading ceases,.ac-

cumulation of effluent within the accumulators 350,

352 also ceases.

When the exterior effluent level drops to a point such that its effective head is less than the effective head of the effluent within the accumulator 350, the valve 366 has unbalanced forces acting on it and therefore opens outwardly to discharge the contents of the accumulator 350. During this time, the valve 372 of the accumulator 352 is held in the closed position and remains in this position until the accumulator 350 has completely emptied and the effective exterior head has dropped below the effective interior head of the accumulator 352. At this point, valve 372 opens and accumulator 352 begins to discharge its contents into the void 354. Thus, the initial excess effluent is accumulated at a higher gravitational potential than would be the case with a single-section accumulator, and the level at which the side walls are wetted is thus maintained at a higher level for a greater length of time than would normally be the case.

So far the accumulators of the present invention have been illustrated and described as having completely enclosed bottom walls so as to retain the effluent within the accumulator until it is released at the appropriate time. It will be understood, however, that even this bottom wall may be eliminated where the bottom face of the soil in which it is placed is of limited permeability either because of the nature of the soil itself or because it is treated to reduce its permeability in connection with the installation of accumulators. In such cases, the limited permeability of the bottom face of the soil serves to retain the effluent in the accumulators during the necessary storage interval, until the effluent level in the exterior void has receded sufficiently to allow discharge of the accumulated contents to the void.

An accumulator of this type is shown in vertical cross section in FIG. 16, in which an accumulator 350 has side walls 352, a roof 354 with a manhole 356 extending through it, effluent inlet channels 358, and an effluent outlet channel 360. A one-way valve 362 is placed in the outlet channel. Effluent distribution channels 364 are formed on the roof of the accumulator for distributing effluent to the void exterior to the accumulator. The operation of this accumulator is essentially the same as was described in connection with FIGS. 1 through 11, that is, effluent is accumulated within the accumulator 350 when the exterior effluent level reaches that of the inlet channel 358 and is discharged therefrom when the exterior effluent level recedes below, the level of the effluent within the accumulator.

Numerous other changes in the various details of the invention set forth above to accomodate the chambers to their environment and to the functions they are to perform will suggest themselves to those skilled in the art, and it is intended that the foregoing be taken as illustrative only, and not in a limiting sense, the scope of the invention being defined with particularity in the claims appended hereto.

CONCLUSION From the foregoing it will be seen that l have provided an improved leaching field in the form of a trench, pit, or bed. The leaching fields of the present invention have substantially the same available infiltrative surface as conventional fields, but require substantially less loading to wet the side wall faces in the case of trenches and pits, and maintain this wetting for a longer period. Further, in the case of leaching trenches, the storage capacity of the trench is substantially increased as compared to that of conventional trenches.

The leaching fields of the present invention are formed with accumulators in the form of hollow casings having one or more fluid inlet channels at the upper portion thereof and one or more fluid outlet channels at the lower portion thereof. The fluid outlet channels restrict fluid inflow by means of valves, restricted orifices, siphons, or the like and operate so as to maintain the effluent exterior to the accumulator at a higher level than it would have in the absence of the accumulator. This insures greater wetting of the side walls than is otherwise obtainable and greater storage capacity for a given wetting level.

The increased wetting of the sidewalls provided in the case of trenches and pits leads to numerous advantages. To begin with, the increased infiltrative capacity encountered in soils having multiple verticallyseparated layers or strata is utilized to the fullest. F urther, elevating the effective level in the field increases the hydrostatic head or hydraulic gradient and thereby increases the effluent infiltration rate. Further, each time the field is dosed with effluent, a substantial volume of air in the field is displaced; as the effluent permeates into the soil, and its level thereby'recedes, fresh air is drawn into the field and this contributes to restoring aeorbic conditions. Additionally, the cyclic raising and lowering of the effluent level in the field assists in sloughing off the biomass which forms on the vertically inclined surfaces, thereby extending the effective filtration life of the sidewall surfaces.

Having illustrated and described the preferred embodiments of my invention, I claim:

1. A structure for placement in a leaching field to which effluent is applied for disposal, said structure comprising an effluent accumulator in the form of a cistern for temporarily storing excess effluent therein and having means forming a fluid transfer channel therein communicating directly with the field surrounding said accumulator and positioned to admit effluent to said accumulator from said field when the level of effluent in said field is above a given level and to discharge effluent therefrom when the level of effluent in said field is below a given level.

2. A structure according to claim 1 in which said means comprises A. at least one generally unrestricted fluid inlet channel communicating between the exterior and interior of said accumulators at an upper portion thereof, and

B. at least one fluid outlet channel communicating between the interior and exterior of said accumulator at a lower end thereof and restricting the inflow of effluent therethrough.

3. A structure according to claim 2 in which said fluid outlet channel includes a valve operable to facilitate effluent outflow but restrict effluent inflow.

14 4. A structure according to'claim 3 in which said valve comprises a flapper valve responsive to the difference in effective hydrostatic head between the interior and exterior of said accumulator to regulate the flow of effluent through the outlet channel.

5. A structure according to claim 1 in which said means comprises A. at least one generally unrestricted fluid inlet channel communicating between the interior and exterior of said accumulator at an upper portion thereof, and B. at least one fluid outlet channel communicating between the interior and exterior of said accumulator at a lower portion thereof and substantially restricted in cross section with respect to the cross section of the fluid inlet channel to thereby restrict the effluent flow rate therethrough 6. A structure according to claim 1 in which said means comprises a fluid channel forming a siphon communicating between the interior and exterior of said accumulator.

7. A structure according to claim 6 in which said siphon is formed from first and second vertically extending fluid channels connected to each other at upper portions thereof and terminating on the interior and exterior, respectively, of said accumulator at lower portions thereof.

8. A structure according to claim 1 in which said accumulator comprises a cistern of generally rectangular cross-section and extended length.

9. A structure according to claim 1 in which said accumulator includes fluid distribution channels formed in an upper portion thereof and extending along the length of said accumulator for carrying effluent from an effluent source and distributing it about the exterior of said accumulator.

10. A structure according to claim 9 in which said channels each include A. a protuberance on one end thereof, and

B. means forming a corresponding recess on the other end thereof for receiving the protuberance of an adjacent accumulator therein, whereby generally continuous distribution channels are formed in accumulators aligned end to end.

11. A structure according to claim 1 in which said accumulator has an inwardly tapering cross-section from the top to the bottom thereof to thereby elevate the center of gravity of effluent therein.

12. A structure according to claim 1 in which said accumulator is constructed to provide greater effluent storage capacity at an upper portion thereof than at a lower portion to thereby elevate the center of gravity of effluent within said accumulator.

13. A structure according to claim 1 comprising upper and lower accumulator sections, and in which said means comprises A. means in said upper section for restricting effluent inflow thereto when the effluent exterior thereof is below a given level, freely admitting effluent to the interior thereof when the effluent is above said level, and discharging effluent therefrom when the exterior effluent level is below the interior effluent level,

B. means in said lower section for discharging effluent therefrom when the exterior effluent level is below the interior effluent level, and

C. fluid-transfer means interconnecting the upper and lower sections for supplying effluent to the lower section from the upper section when the effluent in the upper section exceeds a predetermined level.

14. A structure according to claim 13 in which A. the means in said upper section comprises 1. a relatively unrestricted fluid channel in an upper portion of said section for admitting effluent to the interior of said section, and

2. a fluid outlet channel communicating between the interior and exterior of said section at a lower portion thereof and restricting the inflow of effluent therethrough, and

B. the means in said lower section comprises a fluid outlet channel communicating between the interior and exterior of said section at a lower portion thereof and restricting the inflow of effluent therethrough. v

15. A structure according to claim 14 in which said both fluid outlet channels include valves operable to restrict effluent inflow and provide generally unobstructed effluent outflow.

16. An effluent accumulator temporarily storing therein effluent supplied thereto from a leaching field in which said accumulator is placed and into which said effluent is discharged for disposal, and thereafter releasing it for discharge to said field, said accumulator comprising a generally fluid-impermeable cistern for placement within said field and having A. means defining a relatively unobstructed fluid inlet channel extending between an upper portion of the exterior of said accumulator and the interior thereof for admitting effluent to said accumulator from said field when the fluid level in said field is above that within said accumulator, and

B. means defining a fluid outlet channel extending between a lower portion of the interior of said accumulator and the exterior thereof and constructed to restrict effluent inflow therethrough while providing relatively unobstructed effluent outflow therethrough when the fluid level in said field is below that within said accumulator.

17. An accumulator according to claim 16 which A. has bottom and side walls and a roof defining an enclosed volume for storage of effluent therein,

B. is of generally rectangular cross section and extended length for placement in a leaching trench.

18. An accumulator according to claim 17 including means defining a covered manhole extending through said roof and providing access to the interior of said accumulator.

19. An accumulator according to claim 16 which includes means in said roof defining effluent distribution channels for receiving effluent from a source and distributing it exterior of said accumulator.

20. An accumulator according to claim 16 which is generally cylindrical in shape for placement in a leaching pit.

21. An accumulator according to claim 16 which is of generally rectangular cross section and extended length for placement with a number of similar accumulators side by side and end to end in a leaching bed.

22. An accumulator according to claim 16 which has at least side walls and a roof, said side walls tapering inwardly from said roof.

23. An accumulator according to claim 16 in which said fluid outlet channel includes a valve responsive to the difference in hydrostatic head between the effluent level exterior to said accumulator and that interior 16 thereto to discharge effluent from, and restrict its admission to, said accumulator.

24. A leaching field for the disposal of effluent, comprising A. at least one effluent accumulator for subsurface placement in an excavated void forming said field for periodically storing effluent therein and subsequently discharging it to the void exterior thereof, said accumulator comprising a fluid-confining cistern having flow-regulating means 1. providing a fluid channel communicating between the interior of said accumulator and the field exterior thereto,

2. admitting effluent inflow thereto when the effluent exterior thereof is above a given level,

3. discharging effluent therefrom when the exterior effluent level drops below the interior effluent level, and

B. means for carrying effluent to the void exterior to said accumulator for disposal therein.

25. A leaching field according to claim 24 in which said flow regulating means includes A. means defining an inlet channel extending between the exterior of the accumulator at an upper portion thereof and the interior of the accumulator and supplying effluent to the interior thereof when the exterior effluent level is at or above the level of said channel at the exterior of said accumulator,

B. means defining an outlet channel extending between the interior of said accumulator at a lower portion thereof and the exterior of said accumulator and operable to discharge effluent from the accumulator when the exterior efi'luent level drops below the interior effluent level.

26. A leaching field according to claim 25 which includes a valve responsive to the difference in hydrostatic head between the interior and exterior of said accumulator and positioned within said outlet channel to control effluent flow therethrough.

27. A leaching field according to claim 26 in which said accumulator has a generally rectangular cross section for placement in a leaching trench or bed.

28. A leaching field according to claim 26 in which said accumulator has a generally cylindrical cross-section for forming a leaching pit.

29. A leaching field according to claim 26 in which said accumulator has side walls tapering inwardly from an upper portion thereof to therby store effluent at a higher gravitational potential than in a non-tapered accumulator.

30. A leaching field according to claim 24 in which the means for carrying effluent to said void comprises at least one distributor channel 1. formed integral with said accumulator and extending along the length thereof,

2. adapted to transport effluent therein,

3. in communication with said void over at least one segment intermediate said ends for supplying effluent to said void.

31. A leaching field according to claim 24 in which said accumulator has A. upper and lower fluid-storage sections,

B. an overflow conduit connecting the upper and lower sections and having an upper end thereof terminating in an upper portion of said upper section for passing effluent to said lower section when the effluent in said upper section exceeds a given level.

tween an interior lower portion of the corresponding section and the exterior thereof and each having a valve therein responsive to differences in hydrostatic head between the interior and exterior of the corresponding section for discharging effluent from the corresponding section when the effluent level exterior to said section drops below the effluent level interior thereto. 

1. A structure for placement in a leaching field to which effluent is applied for disposal, said structure comprising an effluent accumulator in the form of a cistern for temporarily storing excess effluent therein and having means forming a fluid transfer channel therein communicating directly with the field surrounding said accumulator and positioned to admit effluent to said accumulator from said field when the level of effluent in said field is above a given level and to discharge effluent therefrom when the level of effluent in said field is below a given level.
 2. A structure according to claim 1 in which said means comprises A. at least one generally unrestricted fluid inlet channel communicating between the exterior and interior of said accumulators at an upper portion thereof, and B. at least one fluid outlet channel communicating between the interior and exterior of said accumulator at a lower end thereof and restricting the inflow of effluent therethrough.
 2. adapted to transport effluent therein,
 2. admitting effluent inflow thereto when the effluent exterior thereof is above a given level,
 2. a fluid outlet channel communicating between the interior and exterior of said section at a lower portion thereof and restricting the inflow of effluent therethrough, and B. the means in said lower section comprises a fluid outlet channel communicating between the interior and exterior of said section at a lower portion thereof and restricting the inflow of effluent therethrough.
 2. second and third fluid channels, in said upper and lower sections, respectively, communicating between an interior lower portion of the corresponding section and the exterior thereof and each having a valve therein responsive to differences in hydrostatic ''''head'''' between the interior and exterior of the corresponding section for discharging effluent from the corresponding section when the effluent level exterior to said section drops below the effluent level interior thereto.
 3. discharging effluent therefrom when the exterior effluent level drops below the interior effluent level, and B. means for carrying effluent to the void exterior to said accumulator for disposal therein.
 3. in communication with said void over at least one segment intermediate said ends for supplying effluent to said void.
 3. A structure according to claim 2 in which said fluid outlet channel includes a valve operable to facilitate effluent outflow but restrict effluent inflow.
 4. A structure according to claim 3 in which said valve comprises a flapper valve reSponsive to the difference in effective hydrostatic head between the interior and exterior of said accumulator to regulate the flow of effluent through the outlet channel.
 5. A structure according to claim 1 in which said means comprises A. at least one generally unrestricted fluid inlet channel communicating between the interior and exterior of said accumulator at an upper portion thereof, and B. at least one fluid outlet channel communicating between the interior and exterior of said accumulator at a lower portion thereof and substantially restricted in cross section with respect to the cross section of the fluid inlet channel to thereby restrict the effluent flow rate therethrough
 6. A structure according to claim 1 in which said means comprises a fluid channel forming a siphon communicating between the interior and exterior of said accumulator.
 7. A structure according to claim 6 in which said siphon is formed from first and second vertically extending fluid channels connected to each other at upper portions thereof and terminating on the interior and exterior, respectively, of said accumulator at lower portions thereof.
 8. A structure according to claim 1 in which said accumulator comprises a cistern of generally rectangular cross-section and extended length.
 9. A structure according to claim 1 in which said accumulator includes fluid distribution channels formed in an upper portion thereof and extending along the length of said accumulator for carrying effluent from an effluent source and distributing it about the exterior of said accumulator.
 10. A structure according to claim 9 in which said channels each include A. a protuberance on one end thereof, and B. means forming a corresponding recess on the other end thereof for receiving the protuberance of an adjacent accumulator therein, whereby generally continuous distribution channels are formed in accumulators aligned end to end.
 11. A structure according to claim 1 in which said accumulator has an inwardly tapering cross-section from the top to the bottom thereof to thereby elevate the center of gravity of effluent therein.
 12. A structure according to claim 1 in which said accumulator is constructed to provide greater effluent storage capacity at an upper portion thereof than at a lower portion to thereby elevate the center of gravity of effluent within said accumulator.
 13. A structure according to claim 1 comprising upper and lower accumulator sections, and in which said means comprises A. means in said upper section for restricting effluent inflow thereto when the effluent exterior thereof is below a given level, freely admitting effluent to the interior thereof when the effluent is above said level, and discharging effluent therefrom when the exterior effluent level is below the interior effluent level, B. means in said lower section for discharging effluent therefrom when the exterior effluent level is below the interior effluent level, and C. fluid-transfer means interconnecting the upper and lower sections for supplying effluent to the lower section from the upper section when the effluent in the upper section exceeds a predetermined level.
 14. A structure according to claim 13 in which A. the means in said upper section comprises
 15. A structure according to claim 14 in which said both fluid outlet channels include valves operable to restrict effluent inflow and provide generally unobstruCted effluent outflow.
 16. An effluent accumulator temporarily storing therein effluent supplied thereto from a leaching field in which said accumulator is placed and into which said effluent is discharged for disposal, and thereafter releasing it for discharge to said field, said accumulator comprising a generally fluid-impermeable cistern for placement within said field and having A. means defining a relatively unobstructed fluid inlet channel extending between an upper portion of the exterior of said accumulator and the interior thereof for admitting effluent to said accumulator from said field when the fluid level in said field is above that within said accumulator, and B. means defining a fluid outlet channel extending between a lower portion of the interior of said accumulator and the exterior thereof and constructed to restrict effluent inflow therethrough while providing relatively unobstructed effluent outflow therethrough when the fluid level in said field is below that within said accumulator.
 17. An accumulator according to claim 16 which A. has bottom and side walls and a roof defining an enclosed volume for storage of effluent therein, B. is of generally rectangular cross section and extended length for placement in a leaching trench.
 18. An accumulator according to claim 17 including means defining a covered manhole extending through said roof and providing access to the interior of said accumulator.
 19. An accumulator according to claim 16 which includes means in said roof defining effluent distribution channels for receiving effluent from a source and distributing it exterior of said accumulator.
 20. An accumulator according to claim 16 which is generally cylindrical in shape for placement in a leaching pit.
 21. An accumulator according to claim 16 which is of generally rectangular cross section and extended length for placement with a number of similar accumulators side by side and end to end in a leaching bed.
 22. An accumulator according to claim 16 which has at least side walls and a roof, said side walls tapering inwardly from said roof.
 23. An accumulator according to claim 16 in which said fluid outlet channel includes a valve responsive to the difference in hydrostatic head between the effluent level exterior to said accumulator and that interior thereto to discharge effluent from, and restrict its admission to, said accumulator.
 24. A leaching field for the disposal of effluent, comprising A. at least one effluent accumulator for subsurface placement in an excavated void forming said field for periodically storing effluent therein and subsequently discharging it to the void exterior thereof, said accumulator comprising a fluid-confining cistern having flow-regulating means
 25. A leaching field according to claim 24 in which said flow regulating means includes A. means defining an inlet channel extending between the exterior of the accumulator at an upper portion thereof and the interior of the accumulator and supplying effluent to the interior thereof when the exterior effluent level is at or above the level of said channel at the exterior of said accumulator, B. means defining an outlet channel extending between the interior of said accumulator at a lower portion thereof and the exterior of said accumulator and operable to discharge effluent from the accumulator when the exterior effluent level drops below the interior effluent level.
 26. A leaching field according to claim 25 which includes a valve responsive to thE difference in hydrostatic head between the interior and exterior of said accumulator and positioned within said outlet channel to control effluent flow therethrough.
 27. A leaching field according to claim 26 in which said accumulator has a generally rectangular cross section for placement in a leaching trench or bed.
 28. A leaching field according to claim 26 in which said accumulator has a generally cylindrical cross-section for forming a leaching pit.
 29. A leaching field according to claim 26 in which said accumulator has side walls tapering inwardly from an upper portion thereof to therby store effluent at a higher gravitational potential than in a non-tapered accumulator.
 30. A leaching field according to claim 24 in which the means for carrying effluent to said void comprises at least one distributor channel
 31. A leaching field according to claim 24 in which said accumulator has A. upper and lower fluid-storage sections, B. an overflow conduit connecting the upper and lower sections and having an upper end thereof terminating in an upper portion of said upper section for passing effluent to said lower section when the effluent in said upper section exceeds a given level.
 32. A leaching field according to claim 31 in which said flow regulating means comprises 